The present invention relates to a sensor coil, in particular for a non-contacting inductive displacement sensor, of the type composed of two, substantially identically formed winding sections, with an unwound section being provided between the two winding sections.
For the purposes of the present invention, a winding section means that a corresponding number of windings of a coil wire are wound over a defined section of the sensor coil. Concretely, it could be, for example, a winding chamber, which can be slid onto a coil form in the way a module. Within the scope of the present invention, the two winding sections are further developed such that they are surrounded by other components, so that for the sake of simplicity, the two winding sections may be called inner winding sections.
Furthermore, the present invention relates to a displacement sensor that comprises a sensor coil of the described type.
The automation of manufacturing processes often requires displacement sensors or displacement measuring systems for measuring short distances. In this connection, it is intended to determine, for example, the position of a moved system component relative to a stationarily arranged component. A typical dimension for such measuring ranges is 50 mm and smaller. Also, another typical requirement on the part of the industry lies in constructing the displacement sensors as compactly as possible in the case of a predetermined measuring range, since the available mounting space is very limited in many cases. This requirement often cannot be met to an adequate extent by the sensors that are currently offered on the market and normally used for short displacement measurements, such as, for example, differential chokes or differential transformers. In these known systems, the overall length amounts to about 2.5 times the measured displacement.
Very often, use is made of non-contacting inductive displacement sensors which operate on the basis of a measuring coil that is energized with alternating current, and an associated, electrically and/or magnetically conductive test object. The market offers corresponding sensors, to which in turn different methods are applied. In this connection, symmetrical systems have been found advantageous with favorable characteristics such as, for example, a temperature response that is relatively easy to compensate. Disadvantageous in these so-called differential systems is the unfavorable ratio of measuring range to overall length of the sensor, i.e., the overall length of the sensor is normally by a multiple greater than the measuring range.
Frequently, there is a demand on the part of the industry for sensors with dimensions that are as compact as possible, in particular in applications which involve large piece numbers. In addition, for purposes of a cost favorable manufacture and easy handling, systems are desirable which need few connection lines in order to keep wiring as simple as possible. Thus, a solution is desirable which fully uses the advantages of symmetric inductive systems and additionally meets with the following requirements:
very compact dimensions of the sensing element;
few connection lines; and
the possibility of simple and economical manufacture.
DE 41 28 159 A1 discloses a sensor coil in the form of a measuring device for determining in a non-contacting manner the displacement or angle of rotation of a component. This sensor coil comprises two winding sections, whose wire windings are wound in a single layer to extend along the longitudinal axis of the coil from the inside outward with a decreasing spacing, i.e., in an inhomogeneous way. The thus formed wire windings permit obtaining a measuring signal with the measuring device disclosed in DE 41 28 159 A1, which has a linear calibration curve over the entire measuring range. This sensor coil has a quite favorable ratio of overall length to measuring range.
In practice, the conversion of the concept of the measuring device disclosed in DE 41 28 159 A1 is complicated and can be realized only with costly manufacturing methods, since the inhomogeneous winding is realizable only with special, costly coil winding machines and only with extensive programming requirements. Thus, it is not possible to realize in small piece numbers an economic production of sensor coils with different characteristics, for example, different windings.
It is therefore an object of the present invention to provide and further develop a sensor coil of the above described known type, which can be produced by simple and economically producible manufacturing methods, and which yet has the advantageous characteristics of the known sensor coil.